I don't have any links per say, but I have done extensive market research on this as it's a requirement in my job (I work at one of the aforementioned open source companies). A quick nitpick, regardless of what people publicly say to the press, I'm 100% positive that most companies are started with some financial motive.

It's not impossible to build a business around open source, but it's incredibly hard. Take MySQL for example. MySQL's initial pitch was this "We'll destroy 50% of the DB market, and then capture 25% of the remaining market." And MySQL the company never really made it. This is with arguably the largest pure technical market to ever exist (databases).